Anybody can produce a number. The hard part — the part that protects you when a client pushes back or a job goes sideways — is producing a number you can stand behind. A defensible estimate does three things a guess never does.
It states its basis
Every estimate rests on assumptions: which scope is included, what quality of materials, what site conditions, which prices and productivity rates. Writing those down is called the basis of estimate. It's the 'show your work' for a price — and it's what lets you explain, later, exactly why the number was what it was.
It owns its accuracy
An estimate built from a napkin sketch cannot be as precise as one built from finished drawings, and pretending otherwise is how contractors lose money. Professional estimators attach an accuracy range to a number based on how complete the design is — a wide range early, a tight range late. A single hyper-precise figure on an early-stage project is a red flag, not a feature.
- Early concept, little detail — expect a wide range and call it a rough order of magnitude.
- Developed design, most decisions made — the range tightens.
- Near-complete documents — the estimate should be close, with little left to assumption.
It says what it excludes
What an estimate leaves out matters as much as what it includes. Permit fees, unforeseen site conditions, owner-supplied fixtures, after-hours work — if they aren't in the number, they need to be named as exclusions. Silent exclusions become arguments. Named exclusions become change orders everyone saw coming.
The goal isn't to be exactly right on day one — nobody is. The goal is to be honest about how right you can be, and to leave a trail that explains the number long after the job is done.